Seventy-nine specimens of a eucrustacean larva (= nauplius) from the Windyfield chert lagerstätte from NE Scotland, which lies near the famous Rhynie chert site, have been investigated. The larvae have already been briefly described before and interpreted as fairy shrimps (Anostraca), a group within Eubranchiopoda, which includes, e.g., tadpole shrimps (Notostraca), clam shrimps ("Conchostraca") and water fleas (Cladocera). Since the larvae are preserved in three dimensions, we could record stacks of images of each specimen under a transmitted light microscope, from which we subsequently produced stereo images. Measurements of different body parts and statistical analyses led to the detection of three size classes, each with exactly the same morphology. Based on our new data, we reject the interpretation that these larvae are fairy shrimp larvae. They are not even eubranchiopod larvae, because the latter have a third limb (= mandible) with only one ramus, while the larvae described here have a biramous mandible. It cannot be excluded that they belong to a species, which derived from the lineage leading towards the Eubranchiopoda, i.e., before Eubranchiopoda had evolved. However, affinities to Maxillopoda are likewise possible, a group that includes, e.g., barnacles, copepods and seed shrimps. There are even morphological similarities to representatives of the thecostracan lineage (barnacles and relatives), but since all known living representatives of this group are fully marine, the interpretation is difficult to substantiate.